1. Field of the Invention
The present invention relates to a stopper and an enclosure cap for a vial incorporating the stopper, and in particular to a cap and stopper that allow multiple piercing.
2. Description of the Related Art
Enclosure caps incorporating elastic stoppers for sealing screw-cap type glass vials are generally known. One prior art enclosure cap is described in U.S. Pat. No. 4,230,231 to Burnett et al. FIGS. 8A and 8B illustrate a prior art cap 110 incorporating a stopper 124 for sealing a vial 116. The stopper 124 has a disk-like upper part and a lower part, the lower part being divided by three equally spaced slots 126 into three flexible equal-length segments 128. The segments 128 surround an interior hollow space 130 which is longer than the slots 126. The stopper 124 is made of an elastic material such as rubber and is bonded to a cap body to form an integral cap 110. When the cap 110 is screwed onto the vial 116, the flexible lower portion of the stopper is inserted into the opening of the vial, thereby sealing the same. The cap body has an opening at the top to expose a central portion of the stopper, allowing piercing through the stopper by a needle to withdraw the liquid contents of the vial.
Such caps are used for air and liquid-tight sealing of a vial while allowing withdrawal of the vial contents by piercing with a needle. Prior to piercing, the vial contents are typically mixed by a rocking motion of the vial. A disadvantage of some prior art enclosure caps is that the contents of the vial may be retained in the hollow portion of the stopper after the rocking motion. Thus, when the stopper is pierced with a single lumen needle, the vial contents that are retained inside the hollow space of the stopper tend to be forced out through the piercing hole around the needle.